1. Field of the Invention
This invention relates to apparatus for remotely repairing and replacing the tubes and tubesheet in a nuclear steam generator, and more particularly to a rotatable tool positioning device forming a part of the apparatus for remotely accurately positioning any of the tools.
2. Description of the Prior Art
Copending patent application Ser. No. 888,701 filed Mar. 21, 1978 of common assignee, discloses a remotely mounted tool support and positioning apparatus for inspecting and repairing the tube and tubesheet of a nuclear steam generator. Generally, this apparatus comprises a horizontally extending tool holder arm cantilevered from a platform which is horizontally movable along a boom and also able to be elevated therefrom. The boom is supported in a manner to permit angular movement in the horizontal plane parallel to the tubesheet. Thus, with the platform being movable radially and vertically and with the boom being movable angularly, a tool disposed in the free or distal end of the tool holder arm can be positioned subadjacent any particular point of the tubesheet and then elevated into proper relationship for accomplishing whatever operation on the tubes or tubesheet is desired. However, because of the internal configuration of the channel head of the generator in which the boom is supported and also because of the configuration of the support of the boom therein, the length of the boom is limited and the travel of the platform therealong is also limited. Therefore, there are certain tubes, i.e., those closest to the divider plate separating the inlet and outlet side of the tubesheet and those tubes closest to the outer wall of the generator, beneath which the platform cannot be disposed. The tool holder arm provides the necessary extension to permit this proper disposition of the tool beneath such tubes; however, the arm must be extending generally radially outwardly to be disposed beneath the outer tubes and generally radially inwardly to be disposed beneath the tubes along the divider plate. Thus, the tool holder arm is manually releasably attached through well known quick release mechanisms to the platform so that when all the necessary operations are accomplished on the tubes or those portions of the tubesheet which are accessible when it extends outwardly, the arm is manually repositioned to extend inwardly for access to the remaining areas and tubes. Thus, under such conditions, minimal exposure to the inside of the generator is required to manually reset the tool arm.
The above operation is generally descriptive of the procedure when the apparatus and tools are being used to remove the tubes and repair and refurbish the tubesheet. However, for retubing operations within the steam generator, the tubes will be installed one column at a time. This means that for each column that is inserted the tool holder arm will have to be changed from one position (i.e., extending outwardly for access to the outermost tubes of that column) to the other position (i.e., extending inwardly for access to the innermost tubes of the column). As there are on the order of 114 columns of tubes, this would require the tool arm to be repositioned 114 times for each individual operation in the retubing procedure. Further, as there are numerous separate operations each requiring a separate tool, such as installing the tubes to the tubesheet, removing the tube guides, positioning the tube ends flush with the tubesheet, and welding the tubes to the tubesheet, all of which may have to be done as each column or several columns is installed, it is evident that manually repositioning the tool holder arm would require extensive exposure to the generator interior.